LETHBRIDGE, Alta. — Alberta's tiny Liberal opposition braced for change Thursday after its leader, Ken Nicol, announced he is jumping to federal politics.

Nicol, who represents Lethbridge East in the Alberta legislature, told a news conference he plans to seek the Liberal nomination in the federal Lethbridge riding. Nicol, 59, said he had a responsibility to deliver the news first to those who voted for him. "I am acting responsibly on behalf of my constituents," he said.

The federal Lethbridge seat is now held by Alliance MP Rick Casson, who got over 22,000 votes more than his Liberal challenger in the 2000 election.

Political observers in the riding say Nicol would be hard-pressed to unseat Casson in the next election, widely expected to be held this spring.

"This has to be one of the strongest Alliance ridings, or now Conservative ridings, in the province . . . so it certainly would be a very tough haul," said Geoffrey Hale, a political science professor at the University of Lethbridge.

"I would think that if Prime Minister (Paul) Martin tried to recruit Mr. Nicol, there would be some quiet promise that the Liberals would look after him at some future time if he isn't successful."

The provincial Liberals will now have to choose a replacement for Nicol. Opposition health critic Kevin Taft has been viewed as one possible successor.

"Under the constitution, a meeting of the board of directors has to be convened and the board has a couple of options," said Jim D'Andrea, president of the Alberta Liberals.

"One option is to appoint an interim leader and/or set a date for a leadership convention."

Another option would be to allow Nicol to remain as leader, at least for a few months.

Nicol took over as leader following the March 2001 provincial election, when Premier Ralph Klein's Tories swept to another huge majority and the Liberals were reduced to seven seats from 18 under then-leader Nancy MacBeth. She resigned within days of the humiliating defeat.

MacBeth had waged an expensive election campaign and the party was left with a $1-million debt and a tiny caucus almost exclusively from Edmonton. Nicol was the only member elected outside the capital city.

Nicol, a farmer with a doctoral degree in economics, left a university teaching job to enter politics and was first elected to the legislature in 1993.

He marked his own way as an Albertan first by breaking with his federal counterparts in opposing the Kyoto accord to reduce greenhouse gas emissions.